fop/fop-core/src/main/java/org/apache/fop/render/ImageHandlerRegistry.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* $Id$ */

package org.apache.fop.render;

import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.apache.xmlgraphics.image.loader.Image;
import org.apache.xmlgraphics.image.loader.ImageFlavor;
import org.apache.xmlgraphics.util.Service;

/**
 * This class holds references to various image handlers. It also
 * supports automatic discovery of additional handlers available through
 * the class path.
 */
public class ImageHandlerRegistry {

    /** the logger */
    private static Log log = LogFactory.getLog(ImageHandlerRegistry.class);

    private static final Comparator<ImageHandler> HANDLER_COMPARATOR
            = new Comparator<ImageHandler>() {
        public int compare(ImageHandler o1, ImageHandler o2) {
            ImageHandler h1 = o1;
            ImageHandler h2 = o2;
            return h1.getPriority() - h2.getPriority();
        }
    };

    /** Map containing image handlers for various {@link Image} subclasses. */
    private Map<Class<? extends Image>, ImageHandler> handlers
            = new java.util.HashMap<Class<? extends Image>, ImageHandler>();
    /** List containing the same handlers as above but ordered by priority */
    private List<ImageHandler> handlerList = new java.util.LinkedList<ImageHandler>();

    private int handlerRegistrations;

    /**
     * Default constructor.
     */
    public ImageHandlerRegistry() {
        discoverHandlers();
    }

    /**
     * Add an PDFImageHandler. The handler itself is inspected to find out what it supports.
     * @param classname the fully qualified class name
     */
    public void addHandler(String classname) {
        try {
            ImageHandler handlerInstance
                = (ImageHandler)Class.forName(classname).newInstance();
            addHandler(handlerInstance);
        } catch (ClassNotFoundException e) {
            throw new IllegalArgumentException("Could not find "
                                               + classname);
        } catch (InstantiationException e) {
            throw new IllegalArgumentException("Could not instantiate "
                                               + classname);
        } catch (IllegalAccessException e) {
            throw new IllegalArgumentException("Could not access "
                                               + classname);
        } catch (ClassCastException e) {
            throw new IllegalArgumentException(classname
                                               + " is not an "
                                               + ImageHandler.class.getName());
        }
    }

    /**
     * Add an image handler. The handler itself is inspected to find out what it supports.
     * @param handler the ImageHandler instance
     */
    public synchronized void addHandler(ImageHandler handler) {
        Class<? extends Image> imageClass = handler.getSupportedImageClass();
        //List
        this.handlers.put(imageClass, handler);

        //Sorted insert (sort by priority)
        ListIterator<ImageHandler> iter = this.handlerList.listIterator();
        while (iter.hasNext()) {
            ImageHandler h = iter.next();
            if (HANDLER_COMPARATOR.compare(handler, h) < 0) {
                iter.previous();
                break;
            }
        }
        iter.add(handler);
        this.handlerRegistrations++;
    }

    /**
     * Returns an {@link ImageHandler} which handles an specific image type given the MIME type
     * of the image.
     * @param targetContext the target rendering context that is used for identifying compatibility
     * @param image the Image to be handled
     * @return the image handler responsible for handling the image or null if none is available
     */
    public ImageHandler getHandler(RenderingContext targetContext, Image image) {
        for (ImageHandler h : this.handlerList) {
            if (h.isCompatible(targetContext, image)) {
                //Return the first handler in the prioritized list that is compatible
                return h;
            }
        }
        return null;
    }

    /**
     * Returns the ordered array of supported image flavors. The array needs to be ordered by
     * priority so the image loader framework can return the preferred image type.
     * @param context the rendering context
     * @return the array of image flavors
     */
    public synchronized ImageFlavor[] getSupportedFlavors(RenderingContext context) {
        //Extract all ImageFlavors into a single array
        List<ImageFlavor> flavors = new java.util.ArrayList<ImageFlavor>();
        for (ImageHandler handler : this.handlerList) {
            if (handler.isCompatible(context, null)) {
                ImageFlavor[] f = handler.getSupportedImageFlavors();
                Collections.addAll(flavors, f);
            }
        }
        return flavors.toArray(new ImageFlavor[flavors.size()]);
    }

    /**
     * Discovers ImageHandler implementations through the classpath and dynamically
     * registers them.
     */
    private void discoverHandlers() {
        // add mappings from available services
        Iterator providers = Service.providers(ImageHandler.class);
        if (providers != null) {
            while (providers.hasNext()) {
                ImageHandler handler = (ImageHandler)providers.next();
                try {
                    if (log.isDebugEnabled()) {
                        log.debug("Dynamically adding ImageHandler: "
                                + handler.getClass().getName());
                    }
                    addHandler(handler);
                } catch (IllegalArgumentException e) {
                    log.error("Error while adding ImageHandler", e);
                }

            }
        }
    }
}